Auto Export Viewport Render to external file
It is called rendering
Exporting images made from 3d scene is called rendering. You can render your 3d scenes to image files. There is no other miraculous secret way of getting images from 3d to a file.  If there was, it would still be called rendering. If you are talking about a process of generating images from a 3d scene and saving them to files that is always called rendering. So you do have rendering functionality in Blender. It is accessible from Blender's Python API as well so writing add-ons that would automatically render and save the viewport is also possible.